<!DOCTYPE html>
<html>
<head>
  <style>
  ul { float:left; margin:5px; font-size:16px; font-weight:bold; }
  p { color:blue; margin:10px 20px; font-size:16px; padding:5px;
      font-weight:bolder; }
  .hilite { background:yellow; }
</style>
  <script src="http://code.jquery.com/jquery-latest.js"></script>
</head>
<body>
  <ul>
    <li style="color:red;">One</li>

    <li style="color:red;">Two</li>
    <li class="hilite">Three</li>
    <li style="color:red;">Four</li>
  </ul>

  <ul>
    <li>Five</li>
    <li>Six</li>
    <li>Seven</li>

  </ul>
  <ul>
    <li style="color:red;">Eight</li>
    <li class="hilite" style="color:red;">Nine</li>

    <li style="color:red;">Ten</li>
    <li class="hilite" style="color:red;">Eleven</li>
  </ul>
  <p>Unique siblings: <b>7</b></p>
<script>

    var len = $(".hilite").siblings()
                          .css("color", "red")
                          .length;
    $("b").text(len);
</script>

</body>
</html>